Projection systems, such as those capable of projecting images onto screens, walls, and the like, are becoming smaller and more compact. By way of example, scanned beam displays employing lasers are becoming small enough to fit in portable electronic devices like palm sized computers, mobile telephones, personal digital assistants and gaming devices. Laser scanned beam displays create brilliant images with vibrant colors. The image quality associated with laser scanned beam displays is unmatched by systems using conventional projection devices. The advent of semiconductor lasers, such as laser diodes, allows these brilliant images to be created by a compact projector, at a reasonable cost, and while consuming small amounts of power.
In a scanned beam display, a mirror coupled to a scanning platform receives light from one or more light sources, such as lasers or light emitting diodes, and scans it in two dimensions along a projection surface to create an image. This scanning is frequently performed in a “raster pattern,” where light is scanned horizontally along one scan axis, referred to as the “fast-scan axis.” Between each fast-scan axis row, the light moves vertically to scan the next row. The vertical scanning movement occurs along a second scanning axis, which is often referred to as the “slow-scan axis.” In ideal raster scanning, a predetermined number of horizontal rows are scanned a predetermined distance apart to form an image.
Scanning perfectly horizontal rows separated by equivalent vertical spaces can be difficult to achieve in compact scanned beam displays. For example, scanning platforms are physical devices that exhibit inertia during movement. This inertia limits physical capabilities of the scanning platform. Designers have learned to work with this inertia to produce images in compact systems by using a sinusoidal scan function to drive the scanning platform. In doing so, an image can be scanned more efficiently.
Image resolution problems can arise, however, when trying to approximate a true raster scan with a sinusoidal waveform. There is thus a need for a scanning device suitable for compact projection systems capable of providing distortion correction.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.